(1) Field of the Invention
The invention relates to a device, systems, and methods for determining the cumulative effects of time and temperature upon matter subjected to heat over a period of time and is directed more particularly to a reusable capsule adapted for use in high-temperature food processing and to systems and methods for establishing the lethality of time and temperature during food processing.
(2) Description of the Prior Art
Thermal processing of foods is directed towards reaching sterility to a selected low level of microbial population, which usually is expressed as "12 log" reductions of the initial microbial population. In most food processing, the pathogenic organism targeted is Clostridium botulinum. It has been established that a 12 log reduction in its population is achieved by heating low-acid foods at 250.degree. F. (121.1.degree. C.) for six minutes, usually stated as a time-temperature integral, or "Fo" of six minutes, or by heating at equivalent time-temperature combinations.
The time-temperature integral, Fo, is computed by integration of the time and temperature of the food product, taking into consideration a temperature sensitivity, or Z "value" of the target organism. Fo is computed from the equation: ##EQU1## wherein T equals the running temperature of the processing operation,
T ref. equals 250.degree. F. (121.1.degree. C.) and PA1 Z=18.degree. F. (10.degree. C.) for C. botulinum spores.
In an everchanging temperature environment during food processing, as in a retort, wherein the temperature of the food particles in a cylindrical can or rectangular tray pack continuously increases to the usually selected value of 250.degree. F. (121.1.degree. C.), the time-temperature integral, Fo, provides an accumulation of lethality units until the heating and cooling of the food is terminated.
In a substantially static situation, as in beef cubes heated in a tray pack, thermocouples are inserted into the center of the cubes to provide an indication of the temperature to which the food particles are heated. The integration of time and temperature with necessary modulation based upon the temperature sensitivity factor Z of the target food microorganism, in accordance with the above equation, provides an indication as to when the target Fo has been reached and therefore when to terminate the processing.
Unfortunately, even under substantially ideal conditions, there are some difficulties, such as site-specific temperature differences, pressure fluctuations during sterilization, and viscosity/thermal conductivity changes of the food particulates. In the case of continuous food processing devices, such as aseptic processing devices, wherein food particles are heated as they are pumped through a heat exchanger, it is not possible to insert thermocouples in the moving food particles to record the time-temperature history of the food particles.
Accordingly, there exists a need during food processing for a time-temperature indicator which can be utilized with continuously flowing foods, as well as relatively static foods and which may be used in high temperature (110.degree.-138.degree. C.) situations.